Abstract

In this study I investigated Procellariiformes (albatrosses, petrels and shearwaters) at sea in the southwestern Atlantic Ocean. Fourteen species and 301 individuals were sampled non-destructively using a cast net method described here. A method is described for ageing Atlantic Yellow-nosed (Thalassarche chlororhynchos) and Black-browed (T. melanophris) Albatrosses based on bill colour and moult. Procellariiformes appear to have two distinct moulting strategies: petrels and shearwaters have complete annual moult, start to moult during the breeding period, and replace several primaries and tail feathers at one time, whereas albatrosses undergo long moulting cycles, replace less feathers at once, and suspend the wing moult during breeding periods. Primary moult starting at P2 rather than P1 was demonstrated to be a common feature in this taxon, with important implications for studies of stable isotopes, trace elements and pollutants in feathers. Overlap between moulting and breeding is demonstrated to be common with tail and contour feathers, but limited in wing, which suggests that flight constraint in long distance foragers rather than nutritional and energetic limitations is the ultimate factor determining primary moult timing. Based on molecular sexing and linear measurements, sexual size dimorphism was shown to vary according to species, with females in general smaller than males, more pronounced in bill measurements than in other traits, and more conspicuous in Giant Petrels (Macronectes spp.) and Diomedea albatrosses. Closely related species pairs of Thallassarche albatrosses and Procellaria petrels had differing levels of sexual dimorphism. The pelagic seabird community sampled comprises birds from different ages and breeding status according to species. Skewed Adult Sex Ratio (ASR) has been proposed as a common pattern in birds, frequently biased towards males and with larger biases in globally threatened species. In albatrosses and petrels, differential mortality of one gender in fisheries is suggested to be caused by sexual size dimorphism giving males a competitive advantage, which allows more access of the larger sex to discards and baits, or to at sea segregation of sexes. These hypotheses were tested by sampling birds at sea and reviewing ASR of birds incidentally captured in fisheries. Skewed ASR is common in albatrosses and petrels from the community attending vessels, but there was no correlation between skewed ASR and conservation status, both in terms of population size or global level of threat, or between ASR and sexual size dimorphism. Thus, sexual dimorphism in size does not explain skewed ASR in the community sampled or in incidental captures in fisheries reported in the review. Differential at sea distributions of males and females appear to explain better the patterns found in the community sampled at sea, as well as skewed ASR in seabird fatalities. Kernel density analysis of satellite tracked Spectacled Petrels (Procellaria conspicillata) in 2006 and 2007 demonstrated intense use of waters in the Brazilian Exclusive Economic Zone, from 26 to 31S, mainly over the continental shelf break and offshore waters. The marine habitats used by Spectacled Petrel and described by bathymetry, SST and productivity are remarkably different from those of the sister species White-chinned Petrel (Procellaria aequinoctialis), which occurs in the area during the winter, but remains over the continental shelf, on Sub-Antarctic and oligotrophic waters. A close association between birds and pelagic longline fishery was demonstrated through comparison of the main kernel areas used by Spectacled Petrels and the pelagic longline fleet. Stable isotopes of nitrogen (δ15N) and carbon (δ13C) in blood preserved in different ways and simultaneously growing feathers were analysed in Spectacled Petrel. Mean δ13C and δ15N values in growing feathers were higher than in blood, suggesting tissue-specific fractionation. Different methods of preserving tissues such as blood may bias stable isotope values. Air drying is proposed as a practical and unbiased method for blood preservation in field situations where freezing is not a practical option, and a mathematical approach is suggested to permit comparison between studies using different preservation methods or tissues. By analysing stable isotopes in blood of all species of Procellariiformes sampled it is demonstrated that availability of discard, mainly the preferred shark liver, which is shared among species with contrasting body masses and feeding techniques, is the ultimate cause of overlapping in trophic levels. Carbon isotopic signature overlapped among the species and was typical of subtropical and offshore region. Early migrant individuals from Antarctica and sub-Antarctic (e.g. Cape Petrel Daption capense, White-chinned Petrel, Wilson’s Storm-petrel Oceanites oceanicus) and species still rearing chicks when sampled (Wandering Albatross Diomedea exulans) had clear carbon isotopic signatures from the austral region. All southern latitude species underwent a clear shift in carbon and nitrogen isotope signatures, increasing in trophic level after arriving in the SW Atlantic. Cory’s Shearwater (Calonectris diomedea), the only species not attending vessels, has low nitrogen values resulting from a diet of flyingfish and squids naturally occurring in the area. While some abundant and widespread petrels and shearwaters, particularly those small in size, benefit from discards from pelagic longline vessels, the balance between benefits and the incidental mortality in hooks is negative for albatrosses and some petrels. Information on bycatch rates of seabirds in the Brazilian domestic pelagic longline fishery from 2001 to 2007 in the Exclusive Economic Zone and adjacent international waters of the southwestern Atlantic Ocean is presented, and bycatch rates for the area are reviewed. Overall, seabird capture rate for the Brazilian pelagic longline fleet was 0.229 birds/1000 hooks, varying from zero to 0.542 birds/1000 according to season. Capture rates were higher between June and November (cold season) and affected mainly the Black-browed Albatross (55% of birds captured), the White-chinned Petrel, the Spectacled Petrel and the Atlantic Yellow-nosed Albatross. Capture rates previously reported in the SW Atlantic varied from 0 to 5.03 birds/1000 hooks, with those based on logbooks or fishermen interviews tending to underestimate capture rates, whereas those based on small numbers of hooks or short time periods tend to greatly overestimate rates in both pelagic and demersal longline fisheries. A range of poorly-known hook-and-line commercial fisheries carried out by the Itaipava fleet, southeastern Brazil, composed by 497 vessels, was described with seven fisheries defined. Capture rates were higher for the surface longline for Dolphinfish (0.15 birds/1000 hooks and 1.08 turtles/1000 hooks), slow trolling for Bigeye Tuna (0.41 birds/day) and handlining targeting Yellowfin Tuna (0.61 birds/day). Bycatch of 47 seabirds, mainly the endangered Spectacled Petrel, Atlantic Yellow-nosed, and Black-browed Albatrosses, and 45 turtles of four species were recorded. Longline and other hook-and-line fisheries are the major threat for albatrosses and petrels from different origins when foraging in the SW Atlantic Ocean, and require urgent conservation measures.